In today's modern society, it has become quite common, and is becoming more so every day, for people to use client-side communication devices referred to generally herein as “access terminals” to communicate wirelessly with and/or via one or more radio access networks (RANs) in order to engage in communication sessions such as voice calls, text messaging, and data sessions with one or more other communication devices. In this disclosure, the term “access terminals” broadly encompasses a wide gamut of types of communication devices that in other contexts may be referred to alternately or additionally as cell phones, smartphones, personal digital assistants (PDAs), mobile stations, mobile devices, user equipment, and the like, and including but not limited to laptop and tablet computers.
Each of the one or more other communication devices with which a given access terminal may be communicating at a given time may be or include another access terminal, an Ethernet-based telephone, a gateway, a server, and/or any other suitable type of communication device. Furthermore, each such other communication device may be arranged to communicate in a wired and/or wireless manner, and may be connected to the same RAN to which the given access terminal is connected, may be connected to a different RAN, or may be connected to some other network such as the Internet or the public switched telephone network (PSTN), as examples. Typically, the RAN to which an access terminal is connected is arranged to directly or indirectly provide connectivity to that access terminal (and other access terminals) with one or more of what are known as “transport networks,” the Internet and the PSTN being two examples.
The wireless communications (e.g., signaling and traffic) between an access terminal and a RAN are typically bi-directional in nature. The portion of those communications that are sent by the RAN to the access terminal are typically described as being sent on the “forward link,” while the portion that are sent by the access terminal to the RAN are typically described as being sent on the “reverse link.” The communications on both links are typically formatted according to a wireless-communication type, protocol, and/or standard, some examples of which include Code Division Multiple Access (CDMA) (e.g., Single Carrier Radio Transmission Technology (1xRTT) CDMA (e.g., IS-95, IS-2000), Evolution Data Optimized (EV-DO) (IS-856)), Time Division Multiple Access (TDMA), Global System for Mobile Communications (GSM), Long Term Evolution (LTE), Wi-Fi (IEEE 802.11), WiMAX (IEEE 802.16), and the like.
With respect to RANs that are of a type often referred to as “wireless wide area networks (WWANs)” or “cellular wireless networks” among other labels, the particular RAN entity with which an access terminal communicates over the air interface is often referred to by terms such as “base station” or “access node,” among others, terms which are used at different times in different ways to refer to different RAN entities or sets of RAN entities. For example, the term “base station” is sometimes used simply to refer to a device often referred to as a “base transceiver station (BTS)” (or “eNodeB”), which contains the hardware, antennas, and so forth that actually conduct the over-the-air portion of the communication with the access terminal on behalf of the RAN. At times, however, the term “base station” or “access node” is used to refer to a combination of (i) one or more BTSs and (ii) a device often referred to as a “base station controller (BSC)” (or “radio network controller (RNC)”), which controls one or more BTS(s) and connects it (them) to the rest of the RAN and typically beyond.
In a typical scenario, an access terminal registers with a RAN via a particular BTS, and then operates in what is known as “idle mode” on a carrier frequency in a coverage area (e.g., a sector) provided by that BTS. If another communication device attempts to contact the access terminal, the RAN will typically page the access terminal via at least that BTS. The access terminal would then typically respond by requesting and establishing communication with the RAN on what is known as an air-interface traffic channel (or simply a “traffic channel”) in order to thereafter conduct the requested communication session over that traffic channel. If instead the access terminal is the initiator of a communication session (perhaps when its user requests a webpage), the access terminal would typically send the RAN what is often referred to as an “access-request message” (or “access probe”) in order to request and establish communication on a traffic channel and then conduct the relevant communication over that traffic channel.
Traffic channels take different forms under different types of air-interface protocols. In TDMA networks for example, traffic channels typically take the form of one or more timeslots of a repeating waveform on a carrier frequency used by multiple access terminals. In other words, in TDMA networks, different access terminals on different traffic channels take turns using the full transmit power of the base station at different times. In CDMA networks by contrast and further by way of example, different access terminals on different traffic channels simultaneously share the transmit power of the base station. In such networks, different traffic channels are delineated by the RAN—on the forward link, and the access terminal on the reverse link—applying different codes (referred to as “spreading codes”) to different communications.